Hitting Rock Bottom

New study shows abundant life feeding on Earth's oceanic crust that may hold clues to origins of lifet

Once thought to be mostly barren, the ocean floor is teeming with life, according to new research. Vast communities of tiny bacteria and other microbes that have existed for more than 3 billion years thrive on deep-sea rocks, yet scientists, including those at Scripps Institution of Oceanography at UC San Diego, are just beginning to understand their self-sufficient lifestyle and link to early life on Earth.

Hubert Staudigel, a research geophysicist at Scripps and co-author of a study published in the May 29 issue of the journal Nature, supplied data from studies of bacteria communities on the Loihi seamount off Hawaii to show just how ubiquitous and abundant microbial life is across the ocean floor.

This discovery supports the notion that bacteria survive on energy from Earth's crust. As new seafloor emerges from mid-ocean ridges, deep-sea microbes quickly colonize; these self-sustaining residents of new ocean "real estate" are considered by scientists to be good candidates as Earth's first colonizers.

"This brings us a step closer to understanding the origin of life," said Staudigel.

According to paper co-author Katrina Edwards, while seafloor microbes have been detected before, this is the first time they have been quantified. Using genetic analysis, Edwards,  a University of Southern California geomicrobiologist, demonstrated that there were thousands of times more bacteria on the seafloor than in the water above.

"We don't know much about what deep-sea bacteria are up to," said Staudigel, who believes that this study helps scientists to better understanding the key players and natural processes that give rise to these communities. Volcanic rocks are emerging as equally complex as farm soil, both sustaining intricate microbial ecosystems that give rise to diverse life.

For more than a decade, researchers including Staudigel have studied geochemical processes in microbial communities at a deep-sea observatory on the Loihi Seamount, the newest island forming off the coast of the Hawaiian Islands. By setting up exposure experiments on the seamount, his research teams can watch which microbes are the first to colonize the new ocean crust and how they turn iron and other chemicals from these deep-sea rocks into food.

These findings underscore how closely linked geologic processes and chemical exchanges are to the development of microbial life in the deep sea, said Donna Blackman, Scripps geophysicist and chair of the NSF Ridge2000 program that partly funded the study and supports interdisciplinary research teams to study ocean ridge communities.

Later this year, Staudigel will set up several new experiments in Antarctica to continue to unravel the mystery of how volcanic rocks give rise to these burgeoning marine microbe communities.

In addition to Staudigel and Edwards, contributors to the paper included lead author Cara Santelli of the Woods Hole Oceanographic Institution (WHOI) and the MIT/WHOIJoint Program in Oceanography and Ocean Engineering and co-authors Erin Banning of the MIT/WHOI Joint Program in Oceanography and Ocean Engineering, Wolfgang Bachof WHOI and Universität Bremen, Craig Moyer of Western Washington University, Mitchell Sogin of the Marine Biological Laboratory at Woods Hole, and Beth Orcutt of the University of Southern California.

—Annie Reisewitz

July/August 2008